Process for shifting the double bond in an olefinic hydrocarbon



United States Patent 3,217,959 PROCESS FOR SEHFTTNG THE DOUBLE BOND INAN GLEFINIC HYBRGCARBQN George L. Hervert, Downers Grove, and Carl E.Linn, Riverside, 111., assignors to Universal Oil Products Company, DesPiaines, 1th, a corporation of Delaware No Drawing. Filed Dec. 4, 1962,Ser. No. 242,089 Claims. (Cl. 260-6832) This application is acontinuation-in-part of our copending application Serial No. 44,249,filed July 21, 1960, now Patent No. 3,114,785.

This invention relates to a process for shifting the double bond of anolefinic hydrocarbon to a more centrally located position in thehydrocarbon chain. More specifically, this invention relates to theshifting of said double bond in the presence of a borontrifluoride-modified substantially anhydrous zirconium oxide.

It is generally well-recognized that the high compression, ignition typeautomobile engines in present day use require fuel of a high anti-knockvalue to give the optimum performance for which they are designed. Theindustry has accorded recognition to the fact that high anti-knockvalues are attributable to the molecular struc ture of the hydrocarbonswhich comprise the gasoline fractions; that highly branched chainhydrocarbons have better anti-knock characteristics than theircorresponding isomers of straight chain or relatively unbranchedstructure.

Motor fuels containing highly branched chain hydrocarbon components maybe produced by the condensation of an isoparaffinic hydrocarbon with anolefinic hydrocarbon in the presence of an acidic acid condensationcatalyst, the process being generally referred to an alkylation. Themore desirable alkylates of this process result from the condensation ofisoparaffins with olefinic hydrocarbons wherein the double bond of saidolefinic hydrocarbon is in a centrally located position of thehydrocarbon chain rather than in a terminal position. Thus, for example,the alkylation of isobutane with Z-butene yields trimethylpentanes withan exceptionally high octane number, whereas l-butene, reactedsimilarly, gives dimethylhexanes which possess a much lower octanerating. One may generalize and state that l-alkenes react with isobutaneto yield dimethylalkanes of poor octane rating.

The olefinic feed stocks generally available for alkylation purposes,and subject to treatment in accordance with the present process, aregenerally a mixture of olefinic hydrocarbons of approximately the samemolecular weight, including both the l-isorner, 2-isomer, and otherposition isomers, capable of undergoing isomerization to an olefin inwhich the double bond occupies a more centrally located position in thehydrocarbon chain. in order to provide an olefinic feed stock foralkylation purposes containing an optimum amount of the more centrallylocated double bond isomers, it is desirable to con vert the l-isomer,or other position isomer, component of the mixed feed stock, into thecorresponding 2-isomer, or into olefins wherein the double bond is morecentrally located in the carbon atom chain. When higher molecular weightolefinic feed stocks are utilized such as hexene, the 1- and 2- positionisomer components are desirably converted into isomers containing thedouble bond located in the 2- and 3-positions.

It is an object of this invention to present a process for shifting thedouble bond of an olefinic hydrocarbon to a more centrally locatedposition in the hydrocarbon chain. It is a more specific object toeifect such shifting of the double bond in the presence of anisomerization catalyst comprising boron trifluoride-modifiedsubstantially anhydrous zirconia.

In one of its broad aspects the present invention embodies a process forshifting a double bond of an olefinic hydrocarbon to a more centrallylocated position in the hydrocarbon molecule, which process comprisesisomerizing said olefinic hydrocarbon at isomen'zation reactionconditions and in contact with an isomerization catalyst comprising aboron trifiuoride-modified substantially anhydrous zirconia.

Other objects and embodiments of the process of this invention willbecome apparent in the following detailed specification.

The olefinic hydrocarbons treated according to the process of thisinvention are hydrocarbons of more than three carbon atoms per moleculeand may be derived from various sources. This process is particularlysuited to the conversion of l-butene to 2-butene. The l-butene may becharged in pure state or in admixture with other hydrocarbons. Thus, amixture containing l-butene as Well as isobutylene, 2-butenes, n-butane,and isobutane, recovered, for example, as the light vapor overheadproduct of a ctalytically cracked gas oil fraction, may be treated inaccordance with the present process. By proper regulation of theisobutane content of such a mixture it will be recognized as a typicalalkylation charge stock. Thus, the process of the present invention maybe utilized for the conversion of the l-butene content in an alkylationcharge stock to the more desirable 2-butene prior to utilization of thecharge in the alkylation process.

The process of this invention can be further utilized to shift thedouble bond of higher molecular weight olefinic hydrocarbons to a morecentrally located position. For example, l-pentene, 3-methyl-1-butene,l-heX- ene, Zahexene, and 4-methyl-l-pentene, can be readily isomerizedto 2-pentene, 3-methy1-2-butene, 2-hexene, 3- hexene, and4-methyl-2-pentene respectively. However, it is not intended to limitthe process of this invention to those enumerated olefins set out aboveas it is contemplated that shifting of the double bond to a morecentrally located position may be effected in straight or branched chainolefinic hydrocarbons containing up to about 20 carbon atoms permolecule according to the process of the present invention.

The description substantially anhydrous, but not completely dry,zirconia, relates to zirconium dioxide which, on a dry basis, containsfrom about 0.1 wt. percent to about 10 wt. percent water in eitherphysical or chemical combination with the zirconium dioxide. This watercontent is determined as volatile matter evolved from the crystallinezirconia upon heating of the same at 900 C. for an extended period, sayfrom about 1 to about 50 hours or more. In contrast to the aluminas, thesubstantially anhydrous, but not completely dry, zirconias, appear tooccur in only one crystalline modification when examined by X-raydiffraction techniques, although the amount of combined water variestherein. The exact reason for the specific utility of crystallinezirconia in the process of this invention is not apparent but isbelieved to be related to the number of residual hydroxyl groupsoccurring on the surface of the zirconia.

The above-described zirconias can be modified with boron trifiuoride byvarious methods. The so-called modification of zirconia with borontrifiuoride is an exothermic process resulting in, for example, aninitial temperature rise to about C. or more when boron trifiuoride ispassed over the zirconia at about room temperature. In general, thezirconia is contacted with boron trifiuoride at a predeterminedtemperature until boron trifiuoride is no longer adsorbed, or otherwisetaken up, by the zirconia. It has been observed that in the treatment ofsubstantially anhydrous zirconias with boron trifluoride, the capacityof the zirconia for boron trifluoride is determined by the particulartemperature at which said treatment takes place, and at a giventemperature, the boron trifiuoride content of the zirconia reaches afixed maximum which is not further increased by contact with additionalquantities of boron trifiuoride at the given temperature. The capacityof zirconia for boron trifiuoride increases with temperature. The exactmanner in which the boron trifiuoride acts to modify the zirconia is notunderstood. It may be that the modification results from the complexingof the boron trifiuoride with the zirconia, or on the other hand, it maybe that the boron trifiuoride reacts with the residual hydroxyl groupson the zirconia surface. In any case, the process of the presentinvention is preferably effected in contact with a catalyst comprising aboron trifiuoride-modified substantially anhydrous zirconia wherein saidzirconia has been thus modified by contact with at least a slight excessof boron trifiuoride at a temperature of from about 50 C. to about 250C.

One suitable method of preparing the boron trifiuoridemodifiedsubstantially anhydrous zirconia comprises placing the substantiallyanhydrous zirconia in a fixed bed located in a suitable reactor andpassing a stream of boron trifiuoride therethro-u'gh. at a preselectedtemperature until such time as boron trifiuoride is no longer adsorbedor otherwise taken up, by the zirconia. When the zirconia is thustreated with boron trifiuoride it is noted that no boron trifiuoridepasses through the zirconia until substantially all of the zirconia hasbeen modified with boron trifiuoride in the manner herein contemplated.The boron trifiuoride stream may be diluted with an inert gas includingnitrogen, hydrogen, helium, or the like, as desired.

The isomerization reaction of the present invention is efiected at atemperature of from about C. to about 250 C. and at a pressure rangingfrom about atmospheric to about 1000 p.s.i. or more. In general, thereactants can be processed in either the liquid or gaseous phase. Incertain cases it may be desirable to maintain the reactants in a liquidphase downflow over the catalyst as a deterent to polymer formationthereon.

One preferred embodiment of the process of the present invention relatesto a process for shifting the double bond of l-butene to produce2-butene which comprises isomerizing said l-butene at an isomerizationtemperature from about 20 C. to about 250 C. and in contact with anisomerization catalyst comprising a boron trifiuoride-modifiedsubstantially anhydrous zirconia.

Another preferred embodiment is in a process for shifting the doublebond of l-pentene to produce Z-pentene which comprises isomerizing saidl-pentene at an isomerization temperature of from about 20 C. to about250 C. and in contact with an isomerization catalyst comprising a borontrifluoride-modified substantially anhydrous zirconia.

Still another preferred embodiment of this invention is in a process forshifting the double bond of a 1-hexene to a more centrally locatedposition, which process comprises isomerizin-g said 1hexene at anisomerization temperature of from about 20 C. to about 250 C. and incontact with an isomerization catalyst comprising a borontrifiuoride-modified substantially anhydrous zirconia.

The present process can be effected in any conventional or otherwiseconvenient manner and may comprise either a continuous or a batch typeof operation. According to one method of operation, the olefinichydrocarbon is continuously charged to a reactor containing therein afixed catalyst bed comprising boron trifiuoride-modified zirconia, thereaction zone being maintained under the reaction conditions previouslydescribed. The reactor efiluent, comprising the isomerization reactionproduct, is continuously withdrawn from the opposite end of the reactorat a rate which will insure an adequate residence time therein. Thehourly space velocity of the olefinic hydrocarbon starting material maybe varied over a relatively Wide range. For example, a gaseous hourlyspace velocity of from about 50 to about 8000 or more is operable in thecase of an olefinic hydrocarbon in the gaseous phase, while olefinichydrocarbons in the liquid phase can be charged at a liquid hourly spacevelocity of from about 0.1 to about 20 or more. However, equilibriumconversion conditions are attained within a more limited range of fromabout 50 to about 4000 space velocity in the case of gaseous olefinichydrocarbons, and from about 0.1 to about 10 space velocity in the caseof liquid olefinic charge stocks.

Other suitable methods, including the moving bed type of operation inwhich the hydrocarbon charge is passed either concurrently orcountercurrently to a moving catalyst bed, or a fluidized system inwhich the hydrocarbon is charged upflow through a dense catalyst phasein a reactor to maintain the catalyst in a state of turbulence underhindered settling conditions, may be utilized. Still another type ofoperation is the slurry or suspensoid type in which the catalyst iscarried as a slurry or suspension into a reaction zone.

In a batch type of operation the olefinic hydrocarbon and the borontrifiuoride-modified zirconia are charged to an autoclave maintained atthe desired temperature and pressure, and the reaction continued untilthe desired degree of isomerization is attained, usually a period of onehour or less. A batch type of operation is particularly suitable whenprocessing a liquid hydrocarbon charge stock comprising olefinichydrocarbons of a relatively high molecular weight, for example, sucholefins as the octenes, nonenes, decenes, etc. In a batch process of theabove type, the catalyst and the olefinic hydrocarbon are preferablymixed during the course of the reaction, for example, by utilizing areactor containing stirring paddles, or a rotating autoclave.

Utilization of the present process to shift the double bond of anolefinic hydrocarbon to a more centrally located position results in anumber of advantages. With respect to the catalyst activity of the borontrifiuoridemodified zirconia, optimum conversion of said olefinichydrocarbon to the desired isomer or isomers thereof is readily obtainedunder mild operating conditions. For example, the Z-butene content of acharge stock, resulting from the conversion of l-butene in contact withsaid boron trifiuoride-modified zirconia at a temperature of about C.,approaches thermodynamic equilibrium composition. In addition themigration of the double bond is not usually accompanied by skeletalrearrangement within the molecule.

The boron trifiuoride-modified zirconia, as utilized in the presentprocess, is characterized by an exceptionally long catalyst life andobviates the necessity of promoters as generally practiced in the priorart. It is contemplated that under extended periods of operation thecatalyst will decline somewhat in activity. However, the nature of thecatalyst is such that it may be readily regenerated simply by passing astream of boron trifiuoride through the catalyst bed, preferably inadmixture with the hydrocarbon charge, thus obviating the necessity ofshutting down the operation to charge a fresh catalyst.

A further advantage to be realized from the utilization of the presentprocess is in the comparative ease with which the catalyst can beprepared and subsequently handled. The transfer of the catalyst requiresonly ordinary precautions against undue exposure to the atmosphere. Onthe other hand, the catalyst can be prepared in situ. For example, thezirconia can be placed in a bed within the reactor subsequently to beused in the isomerization process. The boron trifiuoride is then passedthrough the zirconia bed at a predetermined temperature whereby thedesired catalyst composition is attained. The catalyst thus preparedstands ready for use in the double bond isomerization reaction process.

The following examples are presented in illustration of the specificembodiments of this invention and are not intended as an unduelimitation of the generally broad scope of this invention.

Example I Zirconia was prepared by dissolving zirconium carbonate innitric acid and precipitating zirconium hydroxide by the addition ofammonium hydroxide. The zirconium hydroxide precipitate was filteredfrom the solution, water washed, and dried. After drying, the zirconiumhydroxide became powdery, and it was calcined at a temperature of about650 C. for a period of about hours. X-ray diffraction analysis of thezirconia indicated that it consisted solely of the monocliniccrystalline zirconia containing about 3.20 wt. percent volatile matter(presumably water) which is the weight loss experienced upon heating thezirconia at 900 C.

A portion of the above zirconia was treated with boron trifluoride bypassing the same over the zirconia at 150 C. until boron trifluoride wasobserved in the effiuent gas stream therefrom. After borontrifluoride-modification, the zirconia contained 1.0 wt. percent boronand 1.9 Wt. percent fluorine. It had an apparent bulk density of 1.925g. per ml. and its color was a light grey.

About an 85% conversion of l-butene to the 2-butene isomer thereof iseffected on passing a light vapor overhead from a catalytically crackedgas oil, containing about 25% l-butene, through a fixed bed comprisingabout 60 cc. of the above-described boron trifluoride-modifiedsubstantially anhydrous zirconia, at a gaseous hourly space velocity ofabout 361, an isomerization temperature of about 150 C., and at apressure of about 525 p.s.i.g.

Example 11 This example serves to illustrate the relative inactivity ofboron trifluoride per se with respect to the isomerization of l-buteneas herein contemplated. A normally gaseous hydrocarbon charge stockcomprising 60.7 wt. percent l-butene and admixed with about 365 p.p.m.boron trifluoride based on the total charge, continuously chargedthrough a 60 cc. reaction zone packed with 31 stainless steel helices ata temperature of about 120 C., and at a rate of about 80 g. per hour,resulted in a reaction product substantially as charged and comprising61,.4 wt. percent l-butene.

Example III A charge stock comprising l-pentene, continuously charged toa fixed bed of about 30 grams of the abovedescribed borontrifluoride-modified zirconia at an isomerization temperature of about150 C., at a rate of about 50 g. per hour, and at a pressure of about275 p.s.i.g., is converted to an efiluent stream comprising about of thedesired Z-pentene isomer of said 1- pentene.

Example IV A charge stock comprising l-hexene, continuously charged to afixed bed of about 30 grams of the above-described borontrifluoride-modified zirconia at an isomerization temperature of aboutC., at a rate of about 50 grams per hour, and at a pressure of about 200p.s.i.g., is converted to an effluent stream comprising the 2-hexeneisomer and the 3-hexene isomer of said l-hexene.

We claim as our invention:

1. A process for shifting a double bond of an olefinic hydrocarbon ofmore than three carbon atoms per molecule to a more centrally locatedposition in the hydrocarbon molecule, which consists essentially ofisomerizing said olefinic hydrocarbon in contact with a preformedcombined boron trifluoride-zirconia catalyst prepared by treatingsubstantially anhydrous zirconia with boron trifluoride at a temperatureof from about 50 C. to about 250 C. until boron trifluoride no longercombines with the zirconia.

2. A process for shifting a double bond of an olefinic hydrocarbon ofmore than three carbon atoms per molecule to a more centrally locatedposition in the hydrocarbon molecule, which consists essentially ofisomerizing said olefinic hydrocarbon at an isomerizing temperature offrom about 20 C. to about 250 C. and in contact with a preformedcombined boron trifluoride-zirconia catalyst prepared by treatingsubstantially anhydrous zirconia with boron trifluoride at a temperatureof from about 50 C. to about 250 C. until boron trifluoride no longercombines with the zirconia.

3. The process of claim 2 further characterized in that said olefinichydrocarbon is l-butene.

4. The process of claim 2 further characterized in that said olefinichydrocarbon ig l-pentene.

5. The process of claim 2 further characterized in that said olefinichydrocarbon is l-hexene.

References Cited by the Examiner UNITED STATES PATENTS 2,766,312 10/56Serniuk 260683.15 2,924,629 2/ 60 Donaldson 260 683.2 2,939,890 6/60Hervert et al. 260-671 3,054,834 9/62 Hervert et a1. 260-671 3,114,78512/63 Hervert et al 260683.2

PAUL M. COUGHLAN, Primary Examiner. ALPHONSO D. SULLIVAN, Examiner.

1. A PROCESS FOR SHIFTING A DOUBLE BOND OF AN OLEFINIC HYDROCARBON OFMORE THAN THREE CARBON ATOMS PER MOLECULE TO A MORE CENTRALLY LOCATEDPOSITION IN THE HYDROCARBON MOLECULE, WHICH CONSISTS ESSENTIALLY OFISOMERIZING SAID OLEFINIC HYDROCARBON IN CONTACT WITH A PREFORMEDCOMBINED BORON TRIFLUORIDE-ZIRCONIA CATLYST PREPARED BY TREATINGSUBSTANTIALLY ANHYDROUS ZIRCONIA WITH BORON TRIFLUORIDE AT A TEMPERATUREOF FROM ABOUT 50*C. TO ABOUT 250*C UNTIL BORON TRIFLUORIDE NO LONGERCOMBINES WITH THE ZIRCONIA.